The present invention relates to a sound-absorbing thin-layer laminate according to the precharacterising clause of claim 1, having at least an open-cell backing layer of foam or nonwoven and an open-cell fibre layer, and to a process for the production thereof.
Sound-absorbing thin-layer laminates are used principally in the automobile industry, which is increasingly seeking to produce light, low-cost, low-noise vehicles. This makes it essential to use cheap, thin, light components, which simultaneously exhibit good sound-absorbing properties.
Thus, ultralight sound-insulating vehicle trim is currently known for example from WO-A-98/18656, which is 50% lighter than conventional sound insulation assemblies while retaining identical acoustic efficiency. These sound insulation assemblies substantially comprise an open-cell foam layer, to which a microporous reinforcing layer is applied. In these components, the foam layer, made from thermoformed foam or PU foam, exhibits a thickness of from 10 to 25 mm and the reinforcing layer, made from a thermoplastic mixed fibre nonwoven, exhibit a thickness of from 1.3 to 2.5 mm.
U.S. Pat. No. 5,298,694 describes thin nonwoven laminates for lining vehicle doors. These laminates comprise a nonwoven at least 5 mm thick consisting of thermoplastic fibres and laminated with a thin woven fabric, a fibrous web, a film or a foil. The nonwoven, which is at least 5 mm thick, consists of a mixture of melt-blown microfibres and crimped bulking fibres. Owing to the relatively large diameter of the microfibres (up to 15 xcexcm) and the fact that air flow resistance in the individual layers is not regulated or specified, the sound-absorbing properties of these materials are not optimised and these materials do not take account of sound absorption in particular in relation to lower frequencies.
Air flow resistance may be unambiguously determined using measuring methods as stated in DIN standard 52 213.
Owing to the relatively large diameter of the fibres used (5-15 xcexcm), these nonwoven laminates essentially exhibit a backing function and are distinguished by their mechanical properties, the sound-absorbing performance thereof being rather average.